[milo] Add BuildSummary and common models.

milo/appengine/common/model/status.go

Index: milo/appengine/common/model/status.go
diff --git a/milo/appengine/common/model/status.go b/milo/appengine/common/model/status.go
new file mode 100644
index 0000000000000000000000000000000000000000..7a99fbc9c8b03c3d1d776daa1640c95d3af1007d
--- /dev/null
+++ b/milo/appengine/common/model/status.go
@@ -0,0 +1,63 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+//go:generate stringer -type=Status
+
+package model
+
+import "encoding/json"
+
+// Status is a discrete status for the purpose of colorizing a component.
+// These are based off the Material Design Bootstrap color palettes.
+type Status int
+
+const (
+	// NotRun if the component has not yet been run.
+	NotRun Status = iota // 100 Gray
+
+	// Running if the component is currently running.
+	Running // 100 Teal
+
+	// Success if the component has finished executing and is not noteworthy.
+	Success // A200 Green
+
+	// Failure if the component has finished executing and contains a failure.
+	Failure // A200 Red
+
+	// Warning just like from the buildbot days.
+	Warning // 200 Yellow
+
+	// InfraFailure if the component has finished incompletely due to a failure in infra.
+	InfraFailure // A100 Purple
+
+	// Exception if the component has finished incompletely and unexpectedly. This
+	// is used for buildbot builds.
+	Exception // A100 Purple
+
+	// Expired if the component was never scheduled due to resource exhaustion.
+	Expired // A200 Purple
+
+	// DependencyFailure if the component has finished incompletely due to a failure in a
+	// dependency.
+	DependencyFailure // 100 Amber
+
+	// WaitingDependency if the component has finished or paused execution due to an
+	// incomplete dep.
+	WaitingDependency // 100 Brown
+)
+
+// Terminal returns true if the step status won't change.
+func (s Status) Terminal() bool {
+	switch s {
+	case Success, Failure, InfraFailure, Warning, DependencyFailure, Expired:
+		return true
+	default:
+		return false
+	}
+}
+
+// MarshalJSON renders enums into String rather than an int when marshalling.
+func (s Status) MarshalJSON() ([]byte, error) {
+	return json.Marshal(s.String())
+}